The lepidopteran family Noctuidae includes some of the most destructive agricultural pests, such as the genera Heliothis, Helicoverpa, Spodoptera, and Trichoplusia. For example, included in this family are the tobacco budworm (Heliothis virescens), the cotton bollworm (Helicoverpa zea), the cotton leafworm (Alabama argillacea), the spotted cutworm (Amathes c-nigrum), the glassy cutworm (Crymodes devastator), the bronzed cutworm (Nephelodes emmedonia), the fall armyworm (Spodoptera frugiperda), the beet armyworm (Spodoptera exigua), and the variegated cutworm (Peridroma saucia).
Baculoviruses are arthropod-specific, double stranded DNA viruses that can be used to control insect pests. The nuclear polyhedrosis viruses ("NPV") are one baculovirus subgroup. On the order of forty nuclear polyhedrosis viruses have been isolated from insect species. (See, for example, Atlas of Invertebrate Viruses, Adams and Bonami, editors, CRC Press, Inc., 1991.) Various baculoviruses, including those that infect cotton bollworm, Helicoverpa zea, tobacco budworm, Heliothis virescens, Douglas fir tussock moth, Orygia pseudotsugata, gypsy moth, Lymantria dispar, alfalfa looper, Autographa californica, European pine sawfly, Neodiiprion sertifer, and codling moth, Cydia pomonella, have been registered as pesticides.
A characteristic feature of the NPV group is that many virions are embedded in a crystalline protein matrix referred to as an "occlusion body." Examples of NPVs include Lymantria dispar NPV (gypsy moth NPV), Autographa californica MNPV, Anagrapha falcifera NPV (celery looper NPV), Bombyx mori NPV, Spodoptera littoralis NPV, Spodoptera frugiperda NPV, Heliothis armigera NPV, Mamestra brassicae NPV, Choristoneura fumiferana NPV, Trichoplusia ni NPV, Helicoverpa zea NPV, and Rachiplusia ou NPV. For field use, occluded viruses often are preferable due to their greater stability since the viral occlusion body provides protection for the enclosed infectious nucleocapsids.
Recombinant baculoviruses are also known and useful as insect control compositions. For example, U.S. Pat. No. 5,674,747, issued Oct. 7, 1997, inventors Hammock et al., describes recombinant baculoviruses in which a mutated JHE juvenile hormone esterase) coding sequence provides relatively rapid speed of kill in insects. U.S. Pat. No. 5,674,485, issued Oct. 7, 1997, inventors Hammock et al., describes a recombinant expression vector capable of expression in a host insect and including a coding sequence for JHE that, when expressed, lacks the signal sequence targeting the enzyme to the plasma membrane. U.S. Pat. No. 5,643,776, issued Jul. 1, 1997, inventors Hammock et al., describes recombinant baculoviruses with a mutated JHE coding sequence. McCutchen et al., Bio/Technology, 9, pp. 848-852 (1991), reports the construction of a recombinant, polyhedron-positive Autographa californica NPV that expresses an insect-selective toxin (AaIT), which is isolated from the scorpion Androctonus australis. Copending application Ser. No. 08/435,040, filed May 8, 1995, inventors Hammock et al, describes a method to accelerate the rate of pest kill by treating the pests or their loci with at least two different insect toxins, which are expressed from at least one recombinant microbe such as a baculovirus.
However, a limitation of the use of baculoviruses for pest control has been that their efficacy can be adversely affected by host-plant chemicals and they can also be inactivated by sunlight. The influence of host plants on the course and severity of baculovirus disease in insects has been discussed, for example, by Felton et al. J. Chem. Ecol., 13, pp. 947-957 (1987), J. Chem. Ecol., 16, pp. 1211-1236 (1990), and Arch. Insect Biochem. Physiol, 29, pp. 187-197 (1995). Ignoffo and Garcia, Environmental Entomology, 23, pp. 1025-1029 (1994), have studied the inactivation of microbial insecticides by exposure to sunlight. They found that propyl gallate provided the best protection of Baculovirus heliothis (of three anti-oxidants tested) and catalase the best of three oxidative enzymes tested. They suggested that reactive radicals generated by sunlight can cause inactivation of field-applied viral and other microbial insecticides. Unfortunately, they acknowledged that the materials they had used could not be used practically to provide UV protection of commercial microbial insecticides.